ffmpeg/doc/decoders.texi

   1 @chapter Decoders
   2 @c man begin DECODERS
   3
   4 Decoders are configured elements in FFmpeg which allow the decoding of
   5 multimedia streams.
   6
   7 When you configure your FFmpeg build, all the supported native decoders
   8 are enabled by default. Decoders requiring an external library must be enabled
   9 manually via the corresponding @code{--enable-lib} option. You can list all
  10 available decoders using the configure option @code{--list-decoders}.
  11
  12 You can disable all the decoders with the configure option
  13 @code{--disable-decoders} and selectively enable / disable single decoders
  14 with the options @code{--enable-decoder=@var{DECODER}} /
  15 @code{--disable-decoder=@var{DECODER}}.
  16
  17 The option @code{-decoders} of the ff* tools will display the list of
  18 enabled decoders.
  19
  20 @c man end DECODERS
  21
  22 @chapter Video Decoders
  23 @c man begin VIDEO DECODERS
  24
  25 A description of some of the currently available video decoders
  26 follows.
  27
  28 @section rawvideo
  29
  30 Raw video decoder.
  31
  32 This decoder decodes rawvideo streams.
  33
  34 @subsection Options
  35
  36 @table @option
  37 @item top @var{top_field_first}
  38 Specify the assumed field type of the input video.
  39 @table @option
  40 @item -1
  41 the video is assumed to be progressive (default)
  42 @item 0
  43 bottom-field-first is assumed
  44 @item 1
  45 top-field-first is assumed
  46 @end table
  47
  48 @end table
  49
  50 @c man end VIDEO DECODERS
  51
  52 @chapter Audio Decoders
  53 @c man begin AUDIO DECODERS
  54
  55 A description of some of the currently available audio decoders
  56 follows.
  57
  58 @section ac3
  59
  60 AC-3 audio decoder.
  61
  62 This decoder implements part of ATSC A/52:2010 and ETSI TS 102 366, as well as
  63 the undocumented RealAudio 3 (a.k.a. dnet).
  64
  65 @subsection AC-3 Decoder Options
  66
  67 @table @option
  68
  69 @item -drc_scale @var{value}
  70 Dynamic Range Scale Factor. The factor to apply to dynamic range values
  71 from the AC-3 stream. This factor is applied exponentially.
  72 There are 3 notable scale factor ranges:
  73 @table @option
  74 @item drc_scale == 0
  75 DRC disabled. Produces full range audio.
  76 @item 0 < drc_scale <= 1
  77 DRC enabled.  Applies a fraction of the stream DRC value.
  78 Audio reproduction is between full range and full compression.
  79 @item drc_scale > 1
  80 DRC enabled. Applies drc_scale asymmetrically.
  81 Loud sounds are fully compressed.  Soft sounds are enhanced.
  82 @end table
  83
  84 @end table
  85
  86 @section ffwavesynth
  87
  88 Internal wave synthetizer.
  89
  90 This decoder generates wave patterns according to predefined sequences. Its
  91 use is purely internal and the format of the data it accepts is not publicly
  92 documented.
  93
  94 @section libcelt
  95
  96 libcelt decoder wrapper.
  97
  98 libcelt allows libavcodec to decode the Xiph CELT ultra-low delay audio codec.
  99 Requires the presence of the libcelt headers and library during configuration.
 100 You need to explicitly configure the build with @code{--enable-libcelt}.
 101
 102 @section libgsm
 103
 104 libgsm decoder wrapper.
 105
 106 libgsm allows libavcodec to decode the GSM full rate audio codec. Requires
 107 the presence of the libgsm headers and library during configuration. You need
 108 to explicitly configure the build with @code{--enable-libgsm}.
 109
 110 This decoder supports both the ordinary GSM and the Microsoft variant.
 111
 112 @section libilbc
 113
 114 libilbc decoder wrapper.
 115
 116 libilbc allows libavcodec to decode the Internet Low Bitrate Codec (iLBC)
 117 audio codec. Requires the presence of the libilbc headers and library during
 118 configuration. You need to explicitly configure the build with
 119 @code{--enable-libilbc}.
 120
 121 @subsection Options
 122
 123 The following option is supported by the libilbc wrapper.
 124
 125 @table @option
 126 @item enhance
 127
 128 Enable the enhancement of the decoded audio when set to 1. The default
 129 value is 0 (disabled).
 130
 131 @end table
 132
 133 @section libopencore-amrnb
 134
 135 libopencore-amrnb decoder wrapper.
 136
 137 libopencore-amrnb allows libavcodec to decode the Adaptive Multi-Rate
 138 Narrowband audio codec. Using it requires the presence of the
 139 libopencore-amrnb headers and library during configuration. You need to
 140 explicitly configure the build with @code{--enable-libopencore-amrnb}.
 141
 142 An FFmpeg native decoder for AMR-NB exists, so users can decode AMR-NB
 143 without this library.
 144
 145 @section libopencore-amrwb
 146
 147 libopencore-amrwb decoder wrapper.
 148
 149 libopencore-amrwb allows libavcodec to decode the Adaptive Multi-Rate
 150 Wideband audio codec. Using it requires the presence of the
 151 libopencore-amrwb headers and library during configuration. You need to
 152 explicitly configure the build with @code{--enable-libopencore-amrwb}.
 153
 154 An FFmpeg native decoder for AMR-WB exists, so users can decode AMR-WB
 155 without this library.
 156
 157 @section libopus
 158
 159 libopus decoder wrapper.
 160
 161 libopus allows libavcodec to decode the Opus Interactive Audio Codec.
 162 Requires the presence of the libopus headers and library during
 163 configuration. You need to explicitly configure the build with
 164 @code{--enable-libopus}.
 165
 166 An FFmpeg native decoder for Opus exists, so users can decode Opus
 167 without this library.
 168
 169 @c man end AUDIO DECODERS
 170
 171 @chapter Subtitles Decoders
 172 @c man begin SUBTILES DECODERS
 173
 174 @section dvdsub
 175
 176 This codec decodes the bitmap subtitles used in DVDs; the same subtitles can
 177 also be found in VobSub file pairs and in some Matroska files.
 178
 179 @subsection Options
 180
 181 @table @option
 182 @item palette
 183 Specify the global palette used by the bitmaps. When stored in VobSub, the
 184 palette is normally specified in the index file; in Matroska, the palette is
 185 stored in the codec extra-data in the same format as in VobSub. In DVDs, the
 186 palette is stored in the IFO file, and therefore not available when reading
 187 from dumped VOB files.
 188
 189 The format for this option is a string containing 16 24-bits hexadecimal
 190 numbers (without 0x prefix) separated by comas, for example @code{0d00ee,
 191 ee450d, 101010, eaeaea, 0ce60b, ec14ed, ebff0b, 0d617a, 7b7b7b, d1d1d1,
 192 7b2a0e, 0d950c, 0f007b, cf0dec, cfa80c, 7c127b}.
 193
 194 @item ifo_palette
 195 Specify the IFO file from which the global palette is obtained.
 196 (experimental)
 197
 198 @item forced_subs_only
 199 Only decode subtitle entries marked as forced. Some titles have forced
 200 and non-forced subtitles in the same track. Setting this flag to @code{1}
 201 will only keep the forced subtitles. Default value is @code{0}.
 202 @end table
 203
 204 @section libzvbi-teletext
 205
 206 Libzvbi allows libavcodec to decode DVB teletext pages and DVB teletext
 207 subtitles. Requires the presence of the libzvbi headers and library during
 208 configuration. You need to explicitly configure the build with
 209 @code{--enable-libzvbi}.
 210
 211 @subsection Options
 212
 213 @table @option
 214 @item txt_page
 215 List of teletext page numbers to decode. You may use the special * string to
 216 match all pages. Pages that do not match the specified list are dropped.
 217 Default value is *.
 218 @item txt_chop_top
 219 Discards the top teletext line. Default value is 1.
 220 @item txt_format
 221 Specifies the format of the decoded subtitles. The teletext decoder is capable
 222 of decoding the teletext pages to bitmaps or to simple text, you should use
 223 "bitmap" for teletext pages, because certain graphics and colors cannot be
 224 expressed in simple text. You might use "text" for teletext based subtitles if
 225 your application can handle simple text based subtitles. Default value is
 226 bitmap.
 227 @item txt_left
 228 X offset of generated bitmaps, default is 0.
 229 @item txt_top
 230 Y offset of generated bitmaps, default is 0.
 231 @item txt_chop_spaces
 232 Chops leading and trailing spaces and removes empty lines from the generated
 233 text. This option is useful for teletext based subtitles where empty spaces may
 234 be present at the start or at the end of the lines or empty lines may be
 235 present between the subtitle lines because of double-sized teletext charactes.
 236 Default value is 1.
 237 @item txt_duration
 238 Sets the display duration of the decoded teletext pages or subtitles in
 239 miliseconds. Default value is 30000 which is 30 seconds.
 240 @item txt_transparent
 241 Force transparent background of the generated teletext bitmaps. Default value
 242 is 0 which means an opaque (black) background.
 243 @end table
 244
 245 @c man end SUBTILES DECODERS